A smart entry system described in Patent Literature 1 for example is known as a conventional smart entry system. More specifically, the smart entry system in Patent Literature 1 includes a transmitter that transmits a call signal to a smart key by wireless communication, a receiver that receives a response signal from the smart key responding to the call signal, and an ECU that outputs a call signal transmission command to the transmitter, performs authentication of the response signal when the receiver receives the response signal, and outputs a command for unlocking a door based on an authentication result.
In the above smart entry system, in the case where the call signal from the transmitter is transmitted by a polling system, when a user approaches a vehicle at a predetermined distance, the smart key receives the call signal. Then, the response signal is transmitted from the smart key, and received by the receiver. When the response signal is authenticated by the ECU, the door is unlocked.